Validation of neutron monitor data for studies of cosmic ray modulation

Thesis event information

Date and time of the thesis defence

Place of the thesis defence

Auditorium L2, Linnanmaa Campus, University of Oulu

Topic of the dissertation

Validation of neutron monitor data for studies of cosmic ray modulation

Doctoral candidate

Master of Science Pauli Väisänen

Faculty and unit

University of Oulu Graduate School, Faculty of Science, Space physics and astronomy research unit

Subject of study

Space Physics


Doctor Monica Laurenza, National Institute for Astrophysics (Italy)


Professor Ilya Usoskin, University of Oulu, Sodankylä Geophysical observatory

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Study of cosmic ray variation caused by solar magnetism with neutron monitors

In the doctoral thesis, the modulation of cosmic rays is studied with neutron monitor measurements and a new more precise heliospheric modulation potential is calculated. Neutron monitors are ground based instruments that measure energetic particles. Especially, the neutron monitors can be used to detect cosmic ray particles and their long-term modulation caused by magnetic effects of the Sun. The doctoral thesis studied the periodicities of this modulation. A unique result was that the variation of cosmic rays exhibits turbulent properties. The results help understand and predict solar magnetism, cosmic rays and their effects on Earth and near-Earth space.

As a part of the doctoral research, an extensive and unique survey of global neutron monitor network consisting of about 150 neutron monitors from the 1950s was conducted. This survey revealed important information about the quality and uniformity of different neutron monitor datasets and sources. This resulted in an extensive recommendation list of data sources for each NM station, which will be useful for users of the datasets. The quality and accuracy of the datasets is very important for the reliability and reproducibility of scientific results. In addition to scientific research, the datasets are also for example used for soil moisture measurements in agriculture and estimating the radiation doses of flight and space passengers.

Magnetic effects of the Sun on the cosmic rays can be quantified by the so-called modulation potential, which estimates the average energy loss of energetic particles in the heliosphere. It can be used for example to estimate cosmic ray radiation anywhere on Earth with a few % accuracy. With the high-quality verified neutron monitor dataset and a new computation method a new more precise estimation of the modulation potential was done for the years 1964-2022. This new version was possible to compute and verify in a daily resolution in contrast to earlier versions with only a monthly resolution. The daily resolution will be more useful to be utilized in estimating and predicting space weather effects. The new method is fast and scalable, which makes it possible to easily improve the precision even further and even automate the process in the future.
Last updated: 8.6.2023